The primary function of this laboratory is to evaluate the mutagenicity of particle extracts and chromatographic fractions obtained from atmospheric air samples and combustion effluents, as well as selected pure compounds, in a quantitative forward mutation assay with metabolically competent cell lines derived from human B-lymphoblastoid cells. The primary goal is to identify the major mutagens present and to measure their contribution to the total mutagenicity of the sample. Although the human cell assay is performed under contract at Gentest Corporation (Woburn MA), this Core Laboratory: 1) provides samples for testing, 2) specifies the conditions under which samples are to be tested, 3) interprets the assay data, 4) prepares manuscripts for publication, and 5) participates in the planning of future sample generation and testing efforts. In addition, this laboratory will be involved in the validation of assays with new, genetically engineered cell lines that contain cytochrome P450 forms complementing those found in human lung epithelial cells. Also, effort will be made to optimize the human cell assays by reducing further the culture volume and sample size required.